Fuel tanks within a fuel system of a vehicle have a generally fixed volume in which to maintain fuel. Generally, the maximum fill level for liquid fuel within the fuel tank is controlled by a mechanical shut-off valve that vents the fuel tank. Frequently, this valve is referred to as a fill limit valve. The fill limit valve typically has a float to open and close an orifice in the valve in response to the level of liquid fuel in the tank. When the float reaches a predetermined level indicating the desired maximum fuel level in the fuel tank, the fill limit valve is closed. With the fill limit valve closed it is no longer possible to vent the fuel tank and the pressure inside the tank increases, thereby causing liquid fuel to back-up in a fill tube which actuates an automatic shut-off of a vehicle refueling pump nozzle and terminates the flow of fuel into the tank. The maximum desired fuel level within a vehicle fuel tank is usually less than the total volume of the fuel tank to provide a vapor dome or head space in the tank. The fill limit valve is frequently mounted in that head space in the tank.
Mechanical float valves are typically sized to accommodate the shape and size of the fuel tank in which they are housed. As a result, a mechanical float valve suitable for one fuel tank may not be suitable for another. In addition, generally, mechanical float valves do not provide a repeatable fill level of fuel within the tank from one fill sequence to another. It is not uncommon for a variance of up to one-half gallon or more between the fill sequences.
In addition, fuel tanks typically have additional valves separate from the fill limit valve to provide other venting functions, for example and without limitation, a rollover valve that acts as a vent while open, and automatically closes should the vehicle become inverted to protect against fuel from leaking out of the fuel tank. Having separate valves performing individual functions adds to the complexity and cost of the vehicle fuel system.